| With the rapid development of mobile communication, the application of spread spectrum communication technique in mobile communication field has come into a new age. The spread spectrum communication technique has two forms one is Direct Sequence and the other is Frequency Hopping. Both of them have strong anti-jamming function. Each of them has shortcomings but if they are combined appropriately in Hybrid Spread Spectrum forms DS/FH,the performance of the system and the anti-jamming function can be improved. In this thesis, the author conducted a research on the three forms.Using the DDS chip AD9850 and MCU for core, the spread spectrum signals modulation system is designed. The system can realize three forms of spread spectrum modulation: Direct Sequence, Frequency Hopping and Hybrid Spread Spectrum. Direct Sequence may select two different forms of modulation which are BPSK,QPSK; Frequency Hopping may select different Hop rate and FH Pattern; Hybrid Spread Spectrum may select two modulation scheme that is BPSK,QPSK. This design used MCU as its controller , DDS chip as its modulator and Frequency synthesizer to constitute the hardware terrace of spread spectrum signals modulation system and it realized different scheme of spread spectrum,modulation and FH through software programming. This thesis set forth the internal construction of AD9850; its operational principle; the overall design; the circuit and parameter design of each subsystem. The system circuit of PCB design, setting and debugging are based on these. This thesis displayed the testing result including the spread spectrum scheme and each modulation scheme, and conducted corresponding analyses. The conclusion can be referenced.The experiment shows that the project is of certain practical application value due to the reasonable design of the system and its simple formation, controllable spread spectrum scheme, controllable Frequency Hopping rate ,and the right output waveforms of FH and DS/FH. |
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